The effect of carbohydrate ingestion on gastric emptying, glycogen metabolism, and exercise performance

Abstract:

This study was undertaken to examine the effects of ingestion of different concentrations of carbohydrate (CHO) (H20, 6, 12, and 18 g/100ml- WP, CHO-6, CH0-12, and CH0--18, respectively) on gastric emptying, muscle glycogen metabolism, and performance. Ten trained male cyclists performed four trials of 105 min of continuous cycling at 70% of VO2max. In a fifth trial the subjects completed seven 15-min rides at 70% of VO2max with three min rest between each ride. In all five trials the submaximal rides were followed by an all-out, self-paced 15-min "performance" ride on an isokinetic ergometer (Fitron) interfaced with a computer which calculated the total work output. Every 15 min the men consumed approximately 150 ml (8.5 ml/kg/hr) of one of the four test solutions (in the intermittent trial the men consumed the CHO-12 solution). Blood samples were taken every 15 min for glucose and insulin determination. Muscle biopsies were obtained from the vastus lateralis at 0 and 105 min in the WP, and the CHO-12 continuous and intermittent trials. Biopsy samples were assayed for glycogen, and sectioned and stained for myosin ATPase and glycogen to determine single fiber depletion patterns. Gastric residue was determined by intubation following the performance ride. The volume of drink emptied in the CHO-12 and CHO-18 trials was significantly less compared to both the WP and CHO-6 trials, and the volume emptied in the CHO-18 trial was less than in the CHO-12. There were no differences in glycogen use between the water and the two CHO-12 trials. Single fiber depletion patterns showed a trend toward a greater depletion of type I fibers but were not influenced by CHO ingestion. Blood glucose was significantly elevated at 105 min in both CHO-12 and the CHO-18 trials compared to the WP trial. CHO oxidation in both CHO-12 and the CHO-18 trials was significantly higher in the performance ride. Work output in both the CHO-12 trials was significantly elevated compared to the WP. These data demonstrate that 12 and 18% CHO solutions retarded gastric emptying, but that adequate CHO was delivered to enable enhanced performance in the CHO-12 trials. The fact that glycogen sparing was not observed suggests that the improved performance may have been due to the maintenance of blood glucose. Single fiber depletion patterns did not explain the performance benefits observed with CHO ingestion.